In that case, I'll walk at a pace that's neither fast nor slow, to conserve as much oxygen as possible!

Eos Lumo

How is that different than breathing oxygen?

I lowered the oxygen content in the air around you.

Anyone who uses magic inside these runes will be deprived of oxygen.

Take a deep, long breath and feel the oxygen flowing into every cell in your body.

...I just have to decompose it to create hydrogen and oxygen!

My body doesn't require oxygen, light, or even food.

Nutrition... Oxygen...

Is it my imagination or has the oxygen thinned out a bit?

that your body can't absorb on its own.

Air. The other gases disappeared and oxygen came back.

You thought if you couldn't breathe, all you had to do was bring back the air, but all I got rid of was oxygen.

It's oxygen trapped in a water shell, so you can breath underwater.

I'll put on your oxygen mask now.

Prepare oxygen and an IV.

I did put a ventilator in there,

but if she suddenly woke up, air would run out quickly in a tight space like that.